1. Field of the Invention
This invention relates generally to a video signal display apparatus, and, more particularly, is directed to a video signal display apparatus with a liquid crystal display unit for displaying a video signal reproduced by a video tape recorder (VTR).
2. Description of the Prior Art
A compact video signal display apparatus is known in which a small-sized rotary head VTR and a liquid crystal display unit are integrated in a common housing. The liquid crystal display unit may have a simple matrix system for directly driving the liquid crystal cells by respective matrix electrodes, or an active matrix system may be employed which has switching elements inserted between the liquid crystal cells and the electrodes. Such active matrix system may be of a three-terminal type using transistors as the switching elements, or of a two-terminal type in which non-linear resistance elements, such as, diode rings, back-to-back diodes, or metal-insulated-metal (MIM) diodes are used.
It is desirable that the liquid crystal display unit be capable of displaying a video signal reproduced by a VTR in a variable speed reproducing mode, as well as in a normal reproducing mode. In the variable speed reproducing mode, the VTR reproduces the video signal recorded in slant tracks on a magnetic tape while the tape is being transported at a speed different from that used during recording. For example, in the variable speed reproducing mode, the VTR may effect still reproduction, slow reproduction, double-speed reproduction or high-speed reproduction referred to as cue or review. It is desirable to avoid the generation of noise on the display screen when effecting such variable speed reproduction of the recorded video signal.
In order to improve the recording density by omitting guard bands between the successive slant tracks recorded on the magnetic tape, conventional rotary head VTRs employ at least two heads at diametrically opposed locations on a rotating drum for alternately scanning the successive tracks, with the two heads having differently angled gaps so that different azimuth angles are employed for recording signals in the adjacent tracks. For example, as shown on FIG. 1, a magnetic tape T may have slant tracks A1, A2, . . . in each of which one field of a video signal is recorded by means of a first head with a respective azimuth angle, and which alternate with slant tracks B1, B2 . . . in each of which one field of a video signal is recorded by a second head with a different azimuth angle. In the normal reproducing mode of the VTR, the heads Ha and Hb alternately scan the tape T in the direction indicated by the arrow Xh, while the tape is transported in the direction of the arrow Xt at the normal speed, that is, at the same tape speed as was used during recording, so that the heads Ha and Hb will alternately scan the tracks A1, B1, A2, B2, A3 . . . , respectively. Since the heads used for reproducing fields of the video signal recorded in the several tracks have the same azimuth angles as were used for recording such fields of the video signal in those tracks, the reproduced fields of the video signal have uniformly high levels. Further, since the head scanning any one of the slant tracks for reproducing the video signal field recorded therein has an azimuth angle different from that of the head used in recording the adjacent tracks, cross-talk from such adjacent tracks is minimized.
A number of systems are known for achieving relatively noise-free variable speed reproduction, for example, still reproduction or slow reproduction.
A first system for achieving substantially noise-free variable speed reproduction employs a pair of rotary heads Ha and Hb that are diametrically opposed on the rotary drum DR, as on FIG. 2A, and having relatively broad head widths to extend over two tracks when the drum DR is rotated at the frame frequency, that is, when the rotary drum completes a full revolution in each frame period. In the still reproducing mode, the tape T is stopped at a position in which the trace 40A alternately scanned by the heads Ha and Hb extends over two adjacent tracks A2 and B2.
In a second system for achieving substantially noise-free variable speed reproduction, the rotary head-carrying drum DR again has a pair of diametrically opposed heads Ha and Hb with different azimuth angles, and an additional head Ha' with the same azimuth angle as the head Ha is mounted on the drum DR close to the head Hb, as shown on FIG. 2B. In the still reproducing mode of a VTR according to this second system, the tape T is stopped at a position in which the heads Ha and Ha' alternately scan a trace 40b (FIG. 1) which substantially intersects the center of a track, for example, the track A1, that was recorded by a head having the same azimuth angle as the heads Ha and Ha'.
A third system proposed for achieving noise-free variable speed reproduction converts the reproduced signal into a digital signal which is written into a field memory, and the read out from the field memory is controlled to provide a substantially noise-free reproduced signal. However, this third system is disadvantageous in that it requires A/D and D/A converters, a field memory, a read-out control circuit, and the like which increase the cost, size and power consumption of the corresponding apparatus so that it is difficult to apply such system to a compact, hand-held video reproducing and displaying apparatus.
Noise-free variable speed reproduction with the above-described first and second systems will now be explained with reference to FIG. 3 in which the tape running direction XT is represented by the abscissas and the ordinates represent time, that is, the successive fields Fl, F2, F3 . . . .
In the normal reproducing mode of the VTR embodying the first system, that is, having only the diametrically opposed heads Ha and Hb, such heads Ha and Hb alternately scan the tracks A1, B1, A2, B2, . . . in sequence, as indicated by the obliquely extending line 41 on FIG. 3. When slow reproduction is effected by means of the two heads Ha and Hb, tracking is effected as indicated by the oblique line 42 on FIG. 3. In such case, in order to achieve substantially noise-free slow reproduction, the tape T is transported intermittently, that is, the tape movement undergoes repetitive cycles in each of which the tape is stopped for a predetermined interval and then transported at the normal reproducing speed for another predetermined interval, rather than being merely transported continuously at a speed slower than the tape transporting speed used for recording. The slow-motion ratio is equivalent to the ratio, in each repeated cycle, between the time during which the tape is stopped and the time during which the tap is transported at the normal speed. In the example illustrated by FIG. 3, still reproduction, in which the heads Ha and Hb (indicated at a and b on the drawing for the sake of simplicity) alternately move along the trace 40a on FIG. 1, and thus scan the tracks A2 and B2, is effected in the fields F1-F4 while so-called "frame sending", in which the tape T is transported at the normal speed, is effected during the 4-field period of the fields F5-F8. At the commencement of the next cycle of slow reproduction, still reproduction, in which the heads Ha and Hb alternately scan the tracks A3 and B3, is effected in the field F9 (and of course in the three fields subsequent thereto). The level of the reproduced signal RF1 during the still reproducing phase of the slow reproducing mode gradually increases during each field in which a track recorded with the same azimuth angle as the head Ha, for example, the track A2, is scanned by the head Ha, and the level of the reproduced signal RF1 gradually decreases during each field in which a track recorded with the same azimuth angle as the head Hb, for example, the track B2, is scanned by the head Hb. On the other hand, in the frame sending phase of the slow reproduction mode, the level of the reproduced signal RF1 is not substantially reduced to a small level and, consequently the generation of noise in the picture then reproduced is substantially avoided.
In the case of the second system described above with reference to FIG. 2B and in which three heads Ha, Hb and Ha' are mounted on the rotary drum DR, tracking in the slow reproduction mode is indicated by the oblique line 43 on FIG. 3. Once again, slow reproduction is achieved by means of a repeated cycle involving an interval of still reproduction and an interval or phase of frame sending. In the illustrated example, the interval of still operation occurs until the field F4, with the heads Ha and Ha' alternately scanning the track A1 along the trace 40b on FIG. 1 during such interval with the result that the corresponding reproduced signal RF2 (FIG. 3) has a maximum level at the center of each of the fields F1-F4 and decreases only slightly at the beginning and end of each field. During the frame sending interval of each cycle of slow reproduction, the heads Ha and Hb are alternately operative to scan respective tracks on the tape while the latter is transported at its normal speed, with the result that the level of the reproduced signal RF2 is then almost the same as that achieved in the normal reproducing mode.
In the still reproducing mode of the VTR having three heads Ha, Hb and Ha', the tracking indicated by the oblique line 44 on FIG. 3 is effected, that is, the heads Ha and Ha' alternately scan a track, for example, the track A1, which was recorded by a head having the same azimuth angle as the heads Ha and Ha'.
Further, in the event of a cue/review operation in which the tape T is transported at a high speed in the reverse direction, the tracking indicated by the oblique line 45 on FIG. 3 is effected.
In the case where the slow reproducing mode is achieved by intermittent transporting of the tape at the normal speed while using only the two heads Ha and Hb, as described above, it is difficult to obtain an ample level of the reproduced signal RF1 so that the quality of the reproduced picture is inadequate. Further, since frame reproduction is effected in the still reproducing operation, vibration occurs in the reproduced picture due to a field time difference in the case of pictures containing fast movements. Moreover, in the case of VTRs having two different tape speeds for normal reproducing, for example, for normal play and for extended play, it is difficult to adapt the slow reproducing mode to both tape speeds. More specifically, in this respect, if the head width is determined so that a guard band is not provided between the adjacent tracks when operating at the relatively high or normal tape speed, such head extends over three or more tracks when operating in the extended play mode characterized by a slow tape speed. On the other hand, if the head width is determined so that the head extends over no more than two tracks when using the slow tape speed, then guard bands are produced between the adjacent tracks when using the relatively higher tape speed characteristic of the normal play, thereby making noise-free slow reproduction impossible.
Although the above described system using the rotary drum with the three heads Ha, Hb and Ha' is advantageous, as compared with the system using only two rotary heads, in that the picture quality is improved and field reproduction can be effected, the increased number of heads increases the cost of the apparatus. Furthermore, in the case of VTRs using a small-size rotary drum with four heads thereon instead of the single pair of heads Ha and Hb so as to permit a reduction in the overall size of the VTR, it is very difficult to further increase the number of heads by adding heads corresponding to the head Ha' in FIG. 2B.